REF: Avoid GLib g_memdup deprecation warning on recent Debian

>     src/rule.c:11:5: warning: 'g_memdup' is deprecated: Use 'g_memdup2' instead [-Wdeprecated-declarations]

src/rule.c

@@ -8,7 +8,7 @@
 Rule*
 xsus_rule_copy (Rule *orig)
 {
- Rule *rule = g_memdup (orig, sizeof (Rule));
+ Rule *rule = g_memdup2 (orig, sizeof (Rule));
 
  // Duplicate strings explicitly
  rule->needle_wm_name = g_strdup (orig->needle_wm_name);